POS0496 MANAGEMENT OF OSTEOPOROSIS IN PATIENTS WITH SYSTEMIC MASTOCYTOSIS: A MONOCENTRIC EXPERT CENTRE EXPERIENCE
Authors: C. Nezzar, P. Alary, A. Ruyssen-Witrand, G. Couture, M. Severino-Freire, M. Laroche, A. Constantin, C. Bulai Livideanu, Y. Degboe
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Systemic mastocytosis (SM) is a rare clonal mast cell disease, associated with vertebral osteoporosis (OP) in ~30% of the patients. This OP frequently leads to multiple vertebral fractures, in particular in young or premenopausal patients. To date, experts in the field recommend the use of bisphosphonates as first line therapy [1], or alternatively interferon alfa [2]. However, data regarding treatments efficacy, and regarding the optimal strategy are scarce. Especially, usefulness of mastocytosis-specific treatments is still to be established. <h3>Objectives</h3> To evaluate the clinical and the densitometric efficacy of various treatment regimen for osteoporosis, over 1 year, in patients with systemic mastocytosis. <h3>Methods</h3> We retrospectively analysed demographic, clinical (including new fragility fractures occurrence), biological and densitometric data of patients from our expert centre (CEREMAST), from 2010 to 2022. All patients fulfilled the WHO criteria for systemic mastocytosis and had osteoporosis defined as either a history of fragility fracture or a T-score &lt;-2.5 SD. We evaluated bone mineral density (BMD) by DXA, and the occurrence of fracture, at initiation and after 1 year of exposure to the following treatment for SM-related osteoporosis: interferon alfa 2a (IFN), combination of interferon &amp; monthly pamidronate (IFN+PAM), pamidronate (PAM, monthly in 4 patients, quarterly in 1), masitinib (MASI), and midostaurin (MIDO). IFN+PAM was proposed preferentially to patients with severe osteoporosis and multiple vertebral fractures. PAM was proposed in case of refusal of IFN, or contra-indication to IFN, or additional cause of osteoporosis for which IFN use would not be relevant. Values are reported as mean (+/-SD). Least significant change for BMD was 0.03 g/cm². Baseline and year-1 BMD were compared by a paired t-test. A p-value &lt;0.05 was considered as significant. <h3>Results</h3> We included 37 osteoporotic patients with SM. Thirty-four patients had an indolent SM, 1 had a SM with associated haematological neoplasm, and 2 had an aggressive form. The mean age at diagnosis was 53.5 (+/-12.7) years, with 54.1% of women. Mean lumbar T-score was -2.4 (+/-1.7). Mean hip T-score was -1.8 (+/-0.8). Importantly, 81.1% had history of fragility fractures, and among them 96.6% had vertebral fractures. The mean number of vertebral fractures was 3.6 (+/-3.1) per patient. Two patients were exposed to IFN, 21 to IFN+PAM, 5 to PAM, 2 to MASI, and 9 to MIDO. Among patients treated by MIDO, 2 had prior exposure to IFN+PAM. One patient from the MIDO group and 1 patient from the MASI group were concomitantly exposed to bisphosphonates (respectively alendronate and zoledronate). Regarding treatments efficacy, IFN+PAM and PAM significantly improved BMD (see Figure 1). Two patients treated by IFN+PAM developed an additional vertebral fracture during the first year of follow-up, at 6- and 8-months post-treatment initiation. Importantly, these patients had 4 and 7 vertebral fractures prior treatment. <h3>Conclusion</h3> Our data show that monthly pamidronate, and combination of interferon &amp; pamidronate improve BMD and may reduce fracture risk over 1 year in SM. Conversely, our data do not support the use of interferon monotherapy or midostaurin as preferred strategy in patients with severe osteoporosis. Usefulness of masitinib, and of recent tyrosine kinase inhibitors needs further studies in this population. <h3>References</h3> [1]Rossini, M., et al., Prevalence, pathogenesis, and treatment options for mastocytosis-related osteoporosis. Osteoporos Int, 2016. 27(8): p. 2411-21. [2]Laroche, M., et al., Interferon alpha and pamidronate in osteoporosis with fracture secondary to mastocytosis. Am J Med, 2011. 124(8): p. 776-8. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.